On-demand circuit-switched (CS) network registration

ABSTRACT

Registration of a user equipment (UE) with a circuit-switched (CS) network can be controlled in an “on-demand” fashion by waiting for a trigger event before registering the UE with an available CS network. In some embodiments, CS registration of a UE may be triggered when the mobility management entity (MME) node receives, from the UE, a service request that was sent using Non-Access Stratum (NAS) protocol, such as an extended service request (ESR) or a short message service (SMS) over NAS request. In some embodiments, CS registration of a first UE may be triggered when the MME node receives, from a home subscriber server (HSS), a notification of an incoming session request originating from a second UE to establish a communication session over a CS network with the first UE.

BACKGROUND

Cellular networks are constantly evolving. For example, fifth generation(5G) networks are evolving from fourth generation (4G) Long TermEvolution (LTE) networks, which, in turn, evolved from third generation(3G), and second generation (2G) networks. Because the evolution ofthese technologies takes time, today's cellular networks are“heterogeneous” by employing a mixture of newer (e.g., 5G) and legacy(e.g., 4G/3G/2G) radio access technology (RAT) systems. Although futurecellular networks are likely to remain heterogeneous to some degree, itbecomes cost prohibitive for a carrier to continue to support older RATsystems (e.g., 2G/3G, or circuit-switched (CS) systems) as newer radiotechnologies are brought to market. For this reason, many carriers aregradually phasing out the use of older RAT systems, such as 2G/3G RATsystems that employ a CS network.

As the use of CS networks are phased out, some carriers may leave the CSnetwork intact and available, but may gradually cease to provideparticular services over CS networks. This can cause issues to arisewith user equipment (UEs). For example, if an issue with a preferred RAT(e.g., a 5G or a 4G Long-Term Evolution (LTE) RAT) arises such that a UEis unable to establish a voice-based communication session over thepreferred RAT, the UE may reselect an available CS network, and the UEmay stay “camped” on the CS network indefinitely, or for a long periodof time, even after an available PS network has become available to theUE. When this so-called “CS leakage” occurs across a wide subscriberbase, a large number of UEs can end up utilizing a CS network even whena newer, preferred RAT of a PS network is available to those UEs. Whileconnected to a legacy RAT of a CS network, these UEs cannot availthemselves of the benefits of newer radio technologies (e.g., higherdata transfer rates, better quality audio and/or video, etc.).Furthermore, a carrier may absorb extra costs when their subscribers areutilizing legacy RATs that are being phased out of its network. Theadverse impacts of this issue can be severe, especially considering thevast number of UEs that may be reselecting a CS network, thereby placingsignificant stress on the CS network.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures, in which the left-most digit of a reference number identifiesthe figure in which the reference number first appears. The use of thesame reference numbers in different figures indicates similar oridentical items or features.

FIG. 1 is a diagram illustrating example signaling for implementingon-demand circuit-switched (CS) registration for an originating userequipment (UE) where the CS registration is triggered by an extendedservice request (ESR) from the originating UE.

FIG. 2 is a diagram illustrating example signaling for implementingon-demand CS registration for an originating UE where the CSregistration is triggered by a Short Message Service (SMS) overNon-Access Stratum (NAS) request from the originating UE.

FIG. 3 is a diagram illustrating example signaling for implementingon-demand CS registration for a terminating UE where the CS registrationis triggered by a notification of an incoming session request receivedfrom a Home Subscriber Server (HSS), the incoming session requestrequesting establishment of a communication session over a CS network.

FIG. 4 illustrates a flowchart of an example process for performing CSregistration for a UE, on-demand.

FIG. 5 illustrates a flowchart of an example process for returning a UEback to a PS network after a communication session over a CS network hasterminated.

FIG. 6 illustrates a flowchart of an example process for registering aUE with a CS network based on a capacity metric of the CS network.

FIG. 7 illustrates a flowchart of an example process for establishing acommunication session for a terminating UE that has been registered witha CS network, on-demand.

FIG. 8 is a block diagram of an example system configured to implementon-demand CS registration for a UE.

DETAILED DESCRIPTION

Described herein are, among other things, techniques and systems forcontrolling the registration of a UE with a circuit-switched (CS)network in an “on-demand” fashion, rather than blindly registering theUE with an available CS network immediately in response to receiving acombined attach request from the UE. For example, a mobility managemententity (MME) node of a telecommunications network, may receive acombined attach request from a UE, and may respond to the UE by sendinga message to the UE, the message indicating that the combined attachrequest is accepted. However, instead of registering the UE with anunderlying CS network at the time of receiving the combined attachrequest, the network node waits for a subsequent trigger event beforeregistering the UE with an available CS network.

In some embodiments, CS registration of a UE may be triggered when theMME node receives, from the UE, a service request that was sent usingNon-Access Stratum (NAS) protocol. For example, this service request maybe an extended service request (ESR) received from an originating UE ofa voice-based communication session. The UE may have sent the ESR to theMME node to request to fall back to a CS network in order to establishthe voice-based communication session over the CS network. As anotherexample, the service request may be a short message service (SMS) overNAS request received from the UE when the UE is initiating a data-basedcommunication session (e.g., SMS text messaging session). Accordingly,an example process may include receiving, by a MME node, a combinedattach request from a UE, and sending, by the MME node, to the UE, amessage indicating that the combined attach request is accepted. Theexample process may continue by the MME node receiving a service requestfrom the UE, the service request having been sent using NAS protocol,and, in response, the MME node may register the UE with a CS network.

In some embodiments, CS registration of a first UE may be triggered whenthe MME node receives, from a Home Subscriber Server (HSS), anotification of an incoming session request originating from a second UEto establish a communication session over a CS network with the firstUE. Accordingly, an example process may include receiving, by a MMEnode, a combined attach request from a first UE, and sending, by the MMEnode, to the first UE, a message indicating that the combined attachrequest is accepted. The example process may continue by the MME nodereceiving, from a HSS, a notification of an incoming session requestoriginating from a second UE to establish a communication session over aCS network with the first UE, and, in response, the MME may register theUE with a CS network

By performing on-demand CS registration for UEs, as described herein,one or more devices can be configured to conserve resources with respectto communications bandwidth resources, processing resources, memoryresources, power resources, and/or other resources. For instance, thetechniques and systems described herein may result in a number ofsubscribers and/or UEs registered with a CS network that is less than anumber of subscribers registered with a PS network (e.g., 5G network, a4G LTE network, etc.). In other words, utilization of the CS network maybe kept to a minimum by controlling CS registration per-device by usingan “on-demand” CS registration technique whereby UEs are not registeredwith the CS network unless and until those UEs demand or request (or aredemanded or requested) to utilize the CS network. This conservesresources that would normally be devoted to registering UEs with a CSnetwork, and these resources can, therefore, be made available to otherUEs when those other UEs actually demand (or are demanded to) utilizethe CS network. Furthermore, the techniques and systems described hereindo not require modification of logic on the UE, which means that the UEprocedure for sending a combined attach request and receiving a networkresponse can remain unchanged. Additional technical effects can also berealized from an implementation of the technologies disclosed herein.

In some implementations, the techniques and systems described herein canbe implemented with a 5G network and a 5G-compliant UE, or a 4G LTEnetwork and a 4G-compliant UE. However, the techniques and systems arenot limited to implementations with a 5G network or a 4G network, and aperson having ordinary skill in the art can readily recognize that anycurrent or future radio technology may benefit from the on-demand CSregistration techniques and systems described herein. Accordingly,examples presented herein often refer to a communication session thatutilizes a preferred RAT, such as a “voice over new radio (VoNR)”session/call that utilizes a 5G or a 4G LTE RAT, and which is meant tocover either 5G or 4G LTE sessions (e.g., calls), as well as othercurrent and/or future sessions that use a different radio technologythan 5G or 4G, yet one that can benefit from the techniques and systemsdescribed herein. That said, a VoNR session, as used herein, can bedistinguished from a call that uses a 2G/3G RAT. These and similarpredecessor RATs are referred to herein as, “legacy RATs”.

Also described herein are systems and devices comprising one or moreprocessors and one or more memories, as well as non-transitorycomputer-readable media storing computer-executable instructions that,when executed, by one or more processors perform various acts and/orprocesses disclosed herein.

FIG. 1 is a diagram illustrating example signaling for implementingon-demand circuit-switched (CS) registration for an originating userequipment (UE) 100 where the CS registration is triggered by an extendedservice request (ESR) from the originating UE 100. In accordance withvarious embodiments described herein, the terms “user equipment (UE),”“communication device,” “device,” “wireless communication device,”“wireless device,” “mobile device,” “terminal,” “wireless terminal,”“mobile terminal,” and “client device,” may be used interchangeablyherein to describe any UE (e.g., the UE 100) that is capable oftransmitting/receiving data, wirelessly and/or over wired networks,using any suitable communications/data technology, protocol, orstandard, such as Global System for Mobile Communications (GSM), TimeDivision Multiple Access (TDMA), Universal Mobile TelecommunicationsSystem (UMTS), Evolution-Data Optimized (EVDO), Long Term Evolution(LTE), Advanced LTE (LTE+), Generic Access Network (GAN), UnlicensedMobile Access (UMA), Code Division Multiple Access (CDMA), OrthogonalFrequency Division Multiple Access (OFDM), General Packet Radio Service(GPRS), Enhanced Data GSM Environment (EDGE), Advanced Mobile PhoneSystem (AMPS), High Speed Packet Access (HSPA), evolved HSPA (HSPA+),Voice over IP (VoIP), Voice over LTE (VoLTE), voice over New Radio(VoNR)—e.g., 5G, IEEE 802.1x protocols, WiMAX, Wi-Fi, Data Over CableService Interface Specification (DOCSIS), digital subscriber line (DSL),and/or any future IP-based network technology or evolution of anexisting IP-based network technology.

Furthermore, although the UE 100 is shown as a mobile phone or handsetin FIG. 1, the UE 100 (and other UEs described herein with reference tothe following figures) may be implemented as any suitable type ofcommunication device configured to communicate over a telecommunicationsnetwork, including, without limitation, a mobile phone (e.g., a smartphone) or a handset, a tablet computer, a laptop computer, a portabledigital assistant (PDA), a wearable computer (e.g., electronic/smartglasses, a smart watch, fitness trackers, etc.), an in-vehicle (e.g.,in-car) computer, and/or any similar communication device. In addition,the UE 100 (and other UEs described herein with reference to thefollowing figures) may be a mobile device, or the UE 100 may,alternatively, be a non-mobile (or situated) communication deviceincluding, without limitation, a television (smart television), aset-top-box (STB), a game console, a desktop computer, and the like.

In general, a user can utilize the UE 100 to communicate with otherusers and devices via a telecommunications network. Such atelecommunications network may represent a network comprising aplurality of network nodes disposed between the UE 100 and anotherdevice or user terminal. In some cases, the telecommunications networkmay be inclusive of the other device(s) that is communicating with theUE 100, such as when the UE 100 communicates with an application serveror a similar network node. It is to be appreciated that atelecommunications network over which the UE 100 communicates caninclude any suitable types, and numbers, of network nodes to enable thetransmission of IP multimedia over the telecommunications network. FIG.1 shows at least some suitable network nodes and systems that mayconstitute at least part of the telecommunications network. For example,the telecommunications network may include, without limitation, variousradio access networks (RANs) 102 (e.g., eNodeB, cell towers, wirelessaccess points (APs), etc.). Each RAN 102 may be associated with acorresponding radio access technology (RAT) 104 (e.g., 5G, 4G, 3G, 2G,WiFi, combinations thereof, etc.). The telecommunications network mayfurther include, without limitation, a mobility management entity (MME)node 106, and a mobile switching station (MSS) 108. A person havingordinary skill in the art will readily recognize that atelecommunications network may have several additional nodes thatoperate together to enable the establishment of a communication session,such as nodes of a backhaul network, and/or nodes of a multimediatelephony (MMTel) and IP Multimedia Subsystem (IMS) architecture(sometimes referred to as the “IMS core”, the “IMS core network”, the“IMS network”, the “Core Network (CN)”, or the “IM CN Subsystem”). IMSis an architectural framework defined by the 3^(rd) GenerationPartnership Project (3GPP) for delivering IP multimedia to UEs, such asthe UE 100.

Various portions of the aforementioned telecommunications network,including the MME node 106 and the MSS 108, can be maintained and/oroperated by one or more service providers, such as one or more wirelesscarriers (sometimes referred to as “operators”), that provide IMS-basedservices to users (sometimes called “subscribers”) who are associatedwith UEs (e.g., the UE 100) for accessing the IMS-based services towhich they have subscribed. For example, a service provider may offermultimedia telephony services that allow a subscribed user to call ormessage other users via the telecommunications network using his/her UE100. A user can also utilize an associated UE 100 to receive, provide,or otherwise interact with various different IMS-based services byaccessing the IMS core via various network nodes, such the MME node 106and/or the MSS 108 shown in FIG. 1. In this manner, a carrier may offerany type of IMS-based service(s), such as telephony services (or voicecalling), emergency services (e.g., E911), gaming services, instantmessaging services, presence services, video conferencing services,social networking and sharing services, location-based services,push-to-talk services, WiFi calling services, real time text (RTT)calling services, RTT video calling services, and so on. In order toaccess one or more of these services, the UE 100 is configured torequest establishment of a communication session. Although many of theexamples described herein relate to voice calling services, it is to beappreciated that the UE 100 may request establishment of any type ofcommunication session, such as a data-based communication session (e.g.,SMS text).

Non-Access Stratum (NAS) is a set of protocols in the Evolved PacketSystem. NAS is used for transmitting non-radio signaling between a UE100 and the MME node 106 (e.g., for an LTE/E-UTRAN access). From aprotocol stack perspective, the NAS is the highest stratum of thecontrol plane. NAS procedures can be grouped into two categories: (i)the Evolved Packet System (EPS) Mobility Management (EMM), and (ii) theEPS Session Management (ESM). EMM includes sub-groupings of: (i) EMMspecific procedures, and (ii) EMM connection management procedures. Anattach request (e.g., a combined attach request, as described herein)initiated by the UE 100 is an example of a EMM specific procedure. Aservice request, such as an extended service request (ESR), or a SMSover NAS request, initiated by the UE 100 is an example of a EMMconnection management procedure. Therefore, an attach request, such as acombined attach request, is not a “service request,” as used herein. Asused herein, a “NAS request” is a message that is sent from a UE 100 tothe MME node 106 of the telecommunications network using NAS protocol,and a “NAS response” is a message that is sent from the MME node 106 ofthe telecommunications network to a UE 100 using NAS protocol.

In FIG. 1, at time=t₁, the UE 100 is shown as sending a combined attachrequest 110 to the MME node 106 of the telecommunications network. Forexample, a user of the UE 100 may power-on the UE 100, causing the UE100 to search for a preferred RAN 102(1) to which the UE 100 sends thecombined attach request 110. This combined attach request 110 may besent by the UE 100 as part of a combined attach procedure (e.g., asdefined in 3GPP TS 24.301) to register the UE 100 with both acircuit-switched (CS) network and a packet-switched (PS) network. Such acombined attach request 110 may, for example, request that the UE 100 beregistered with a PS network (e.g., a 5G network, a 4G LTE network,etc.) for evolved packet system (EPS) services, and also with a CSnetwork (e.g., a 2G/3G network) for non-EPS services (sometimes referredto as “International Mobile Subscriber Identity (IMSI) attached”). Thecombined attach request 110 may be sent via a first RAN 102(1), such asa RAN 102(1) that is associated with a preferred RAT 104(1) (e.g., a 5GRAT, a 4G LTE RAT, etc.). The combined attach request 110 may betransmitted using NAS protocol, such that the request 110 may beconsidered a NAS request.

The MME node 106 receives, via the first RAN 102(1), the combined attachrequest 110 from the UE 100, and responds by sending, to the UE 100, amessage 112 that acknowledges receipt of the request 110, and thatprovides an attach result (e.g., “attach accepted: combined”, “attachaccepted: EPS only”, or “attach rejected”). In the example of FIG. 1,the message 112 indicates that the combined attach request 110 isaccepted (e.g., attach accepted: combined). Of course, depending on thecircumstances, the message 112 may include other attach results in thealternative, such as an attach result of “EPS only”—if, for example, anunderlying CS network is unavailable to the UE 100, or an attach resultof “Rejected”—if, for example, the MME node 106 (or another networknode) determines that there is, or will be, an issue registering witheither type of network. FIG. 1 assumes that both a PS network (e.g., apreferred RAT 104(1), such as a 5G RAT, a 4G LTE RAT, etc.) and a CSnetwork (e.g., a legacy RAT 104(2), such as a 2G/3G RAT) are availableto the UE 100 at time=t₁, when the UE 100 sends the combined attachrequest 110 to the MME node 106. This results in the MME node 106sending, and the UE 100 receiving, a message 112 indicating that thecombined attach request 110 is accepted.

At 114 of FIG. 1, at time=t₁, when the UE 100 sends the combined attachrequest 110 to the MME node 106, the MME node 106 refrains fromregistering the UE 100 with the CS network, or, if the UE 100 happens tobe registered with the CS network when the combined attach request 110is received, the MME node 106 may de-register the UE 100 from the CSnetwork at 114. That is, the MME node 106 may determine whether the UE100 is, or is not, presently registered with the CS network at 114(e.g., by accessing a registry of UEs registered with the CS network),and, if registered, the MME node 106 may de-register the UE 100 from theCS network at 114. Regardless of whether the MME node 106 refrains fromregistering the UE 100 with the CS network or de-registers the UE 100from the CS network, the lack of CS registration of the UE 100 occursdespite the availability of a CS network (e.g., RAN 102(2) associatedwith RAT 104(2), such as a 2G/3G RAT) and despite the sending of themessage 112 indicating that the combined attach request 110 is accepted.In other words, the MME 106 is configured to “fake” the combined attachprocedure by indicating to the UE 100 that the UE 100 is registered witha CS network when, in fact, the UE 100 is not registered with a CSnetwork.

Avoiding CS registration of the UE 100 at 114 may help manage thecapacity of the CS network (e.g., conserve resources of the CS network)by keeping the UE 100 unregistered with respect to the CS network,thereby leaving resources of the CS network unreserved/available forother UEs that actually demand utilization of those resources when theCS network is utilized. Avoiding CS registration of the UE 100 at 114may also avoid so-called “CS leakage” by preventing the UE 100 fromending up “camped” on the CS network indefinitely (or for a long periodof time), as described above, notwithstanding availability of apreferred, PS network (e.g., a 5G network, a 4G LTE network, etc.).Using the techniques and systems of FIG. 1, the MME node 106 does notblindly register the UE 100 with the CS network. Instead, the MME node106 waits to register the UE 100 with the CS network until a time atwhich the UE 100 actually demands utilization of the CS network (e.g.,to establish a communication session). In practice, a vast majority ofUEs 100 s may seldom, or never, demand utilization of the CS network aslong as a preferred RAT 104(1) of a PS network is, and remains,available to the UE 100. However, in some instances, a UE 100 may beconfigured to request utilization of a CS network, such as if apreferred, PS network is unavailable at a time when the UE 100 is tryingto establish a voice-based communication session with another endpoint(e.g., another UE, a public safety answering point (PSAP), etc.). FIG. 1illustrates one example trigger event that may cause the UE 100 to beregistered with an available CS network in an on-demand fashion.

In FIG. 1, at time=t₂, the UE 100 is shown as sending an extendedservice request (ESR) 116 to the MME node 106. The ESR 116 may be sentvia the first RAN 102(1), which, again, may be a RAN 102(1) that isassociated with a preferred RAT 104(1) (e.g., a 5G RAT, a 4G LTE RAT,etc.). The ESR 116 may be transmitted using NAS protocol, such that therequest 116 may be considered a NAS request. An “extended servicerequest (ESR)” is a message that is sent by a UE 100 to the MME node 106in order to request a circuit-switched fallback (CSFB) procedure, forexample, indicating that the UE 100 had attempted to establish acommunication session over the PS network and is requesting to fall backto the CS network. For example, the UE 100 may be an originating UE 100(sometimes referred to as “MO UE” 100, “MO” meaning “mobile originated”or “mobile originating”) of a communication session, meaning that theoriginating UE 100 is initiating the communication session (e.g., a userof the UE 100 may have dialed a phone number of a called party). An ESRcan be triggered at the UE 100 by various events. For example, a UE 100that does not have a voice-over IP (VoIP) capability or that has a VoIPcapability disabled in user settings may send a ESR 116 to the MME node106 when the user of the UE 100 makes a call by dialing a phone number.As another example, the UE 100 may start a timer while setting up a VoIPcall over a preferred RAT 104(1) of a PS network, and if a timeoutoccurs before the UE 100 receives an expected network response, the UE100 may send a ESR 116 to the MME node 106. As yet another example, anetwork node may send a signal to the UE 100 indicating that a VoIP callcannot be established.

The MME node 106 may receive, via the first RAN 102(1), the ESR 116 fromthe UE 100, and, at 118, the receipt of the ESR 116 from the UE 100triggers the MME node 106 to register the UE 100 with the CS network. Inother words, by sending the ESR 116 to the MME node 106, the UE 100 isinforming the MME node 106 that the UE 100 wants to utilize the CSnetwork for a communication session. Accordingly, in response toreceiving the ESR 116 from the UE 100, the MME node 106 may perform CSregistration 120 by registering the UE 100 with the CS network.

In some embodiments, one or more additional criteria are evaluatedbefore registering the UE 100 with the CS network. For example, acurrent utilization of the CS network may be evaluated to determine ifthere is capacity or bandwidth in the CS network to handle theto-be-registered UE 100. For example, in response to receiving the ESR116 from the UE 100, a determination may be made as to a number of UEs(and/or subscribers associated therewith) currently registered with theCS network, and the CS registration 120 may be performed for the UE 100based at least in part on the number of UEs currently registered withthe CS network. For example, the number of UEs currently registered withthe CS network may be compared to a threshold number, and if the numberof presently-registered UEs satisfies (e.g., meets, meets or exceeds)the threshold number, the UE 100 may not be registered with the CSnetwork due to limitations in bandwidth or capacity of the CS network tohandle additional UEs. If, however, the number of presently-registeredUEs does not satisfy (e.g., does not meet, meets but does not exceed)the threshold number, the UE 100 may be registered with the CS network(i.e., CS registration 120 may be performed).

In some embodiments, the CS registration 120 of the UE 100 (i.e.,registering the UE 100 with the CS network) may include sending, by theMME node 106, an identifier (ID) 122 associated with the UE 100 to theMSS 108. The MME node 106 may further receive information 124 from theMSS 108 that is usable to establish a communication session over the CSnetwork. In some embodiments, the MME node 106 may send, to the UE 100,a message 126 indicating that the ESR 116 is accepted. This message 126may include the information 124 the MME node 106 received from the MMS108, which is usable by the UE 100 to establish the communicationsession over the CS network. For example, the information 124—receivedfrom the MSS 108 and forwarded by the MME node 106 to the UE 100—mayinclude an identifier and/or an address of the RAN 102(2) associatedwith a legacy RAT 104(2) of the CS network, which allows the UE 100 toredirect 128 from the preferred RAN 102(1) to the RAN 102(2) associatedwith a legacy RAT 104(2) (e.g., 2G/3G RAT) of the CS network. This maycause the UE 100 to switch from a voice-over IP (VoIP) call to a CScall, for example. The RAN 102(1) may redirect 128 the UE 100 to the RAN102(2), such as by sending an Inter RAT (IRAT) handover command to theUE 100, by cell reselection, or any other suitable redirection 128technique.

The UE 100 may conduct the communication session over the CS networkusing the legacy RAT 104(2), and when the communication session isterminated, such as when a user hangs up a call, a network node (e.g.,the MSS 108, the RAN 102(2), etc.) and/or logic of the UE 100 may causethe UE 100 to return 130 to the preferred RAN 102(1) associated with thepreferred RAT 104(1) of the PS network. This so-called “fast return” 130logic redirects the UE 100 to the PS network and prevents the UE 100from staying camped on the legacy RAT 104(2) for longer than it needs tobe there. That is, once the UE 100 is finished using the legacy RAT104(2) of the CS network for the communication session, the UE 100 isredirected back (e.g., via return 130) to the preferred RAT 104(1) ofthe PS network.

It can be appreciated that the techniques and systems described withreference to FIG. 1 allow for better management of the capacity of alegacy CS network, which may help while phasing out a CS network from acarrier's network infrastructure. For instance, the techniques andsystems of FIG. 1 may result in a number of subscribers registered witha CS network that is less than a number of subscribers registered with aPS network (e.g., a 5G network, a 4G LTE network, etc.). In other words,utilization of the CS network may be kept to a minimum by controlling CSregistration 120 per-device by using an “on-demand” CS registrationtechnique where UEs 100 are not registered with the CS network unlessand until those UEs 100 demand or request utilization of the CS network.The techniques shown in FIG. 1 is useful for voice-based communicationsessions, such as phone calls, where the UE 100 is attempting toestablish a 5G Voice-over IP (VoIP) call using a 5G RAT, or a Voice-overLTE (VoLTE) call using a 4G LTE RAT (e.g., RAT 104(1)) of a PS network,and the UE 100 sends an ESR 116 to request an extension of service to aCS network, thereby triggering the CS registration 120 at 118 andredirecting the UE 100 to a RAN 102(2) associated with a legacy RAT104(2) (e.g., a 2G/3G RAT) of the CS network.

FIG. 2 is a diagram illustrating example signaling for implementingon-demand CS registration for an originating UE 200 where the CSregistration is triggered by a Short Message Service (SMS) overNon-Access Stratum (NAS) request from the originating UE 200. It is tobe appreciated that the UE 200 may be similar to the UE 100 describedherein. Furthermore, the RANs 202 may be similar to the RANs 102described herein. Furthermore, the RATs 204 may be similar to the RATs104 described herein. Furthermore, the MME node 206 may be similar tothe MME node 106 described herein. Furthermore, the MSS 208 may besimilar to the MSS 108 described herein.

In FIG. 2, at time=t₁, the UE 200 is shown as sending a combined attachrequest 210 to the MME node 206 of the telecommunications network. Forexample, a user of the UE 200 may power-on the UE 200, causing the UE200 to search for a preferred RAN 202 to which the UE 200 sends thecombined attach request 210. This combined attach request 210 may besimilar to the combined attach request 110 described herein.

The MME node 206 receives, via the RAN 202, the combined attach request210 from the UE 200, and responds by sending, to the UE 200, a message212 that acknowledges receipt of the request 210, and that provides anattach result (e.g., “attach accepted: combined”, “attach accepted: EPSonly”, or “attach rejected”). In the example of FIG. 2, like FIG. 1, themessage 212 indicates that the combined attach request 210 is accepted(e.g., attach accepted: combined). Of course, depending on thecircumstances, the message 212 may include other attach results, asdescribed with reference to FIG. 1.

At 214 of FIG. 2, at time=t₁, when the UE 200 sends the combined attachrequest 210 to the MME node 206, the MME node 206 refrains fromregistering the UE 200 with the CS network, or, if the UE 200 happens tobe registered with the CS network when the combined attach request 210is received, the MME node 206 may de-register the UE 200 from the CSnetwork at 214. That is, the MME node 206 may determine whether the UE200 is, or is not, presently registered with the CS network at 214(e.g., by accessing a registry of UEs registered with the CS network),and, if registered, the MME node 206 may de-register the UE 200 from theCS network at 214. Regardless of whether the MME node 206 refrains fromregistering the UE 200 with the CS network or de-registers the UE 200from the CS network, the lack of CS registration of the UE 200 occursdespite the availability of a CS network (e.g., a 2G/3G RAT) and despitethe sending of the message 212 indicating that the combined attachrequest 210 is accepted. In other words, the MME 206 is configured to“fake” the combined attach procedure by indicating to the UE 200 thatthe UE 200 is registered with a CS network when, in fact, the UE 200 isnot registered with a CS network.

In FIG. 2, at time=t₂, the UE 200 is shown as sending a SMS over NASrequest 216 to the MME node 206. The SMS over NAS request 216 may besent via the RAN 202, which may be a RAN 202 that is associated with apreferred RAT 204 (e.g., a 4G LTE RAT). The SMS over NAS request 216, asits name implies, may be transmitted using NAS protocol, such that therequest 216 may be considered a NAS request. This SMS over NAS request216 may be an Uplink NAS Transport message sent by a UE 200 to the MMEnode 206 in order to request sending a SMS text message with a NASmessage for transport, instead of using an IP-based message. A SMS overNAS request 216 can be triggered at the UE 200 by various events. Forexample, a UE 200 that does not have a capability for sending SMS overIP or that has such a capability disabled in user settings may send aSMS over NAS request 216 to the MME node 206 when the user of the UE 200opens a SMS text messaging application, enters text, and tries to sendthe SMS text message. As another example, the UE 200 may start a timerwhile attempting to send a SMS text message over IP signaling of apreferred RAT 204 of a PS network, and if a timeout occurs before the UE200 receives an expected network response, the UE 200 may send a SMSover NAS request 216 to the MME node 206. As yet another example, anetwork node may send a signal to the UE 200 indicating that SMS over IPcannot be supported. Accordingly, this SMS over NAS request 216 mayindicate that the UE 200 had attempted to send (or establish aconnection for sending) a SMS text message over IP signaling of the PSnetwork and is requesting to fall back to “the CS network.” CS networkis in quotations here to denote the fact that the UE 200 will not haveto actually redirect to a legacy RAN of a CS network to send the SMStext message(s). Rather, the UE 200 can stay attached to the preferredRAN 202 and may send the SMS text message(s) over NAS signaling via thepreferred RAN 202 associated with a preferred RAT 204 (e.g., a 4G LTERAT). That said, the UE 200 may still be required to register with theCS network for sending SMS text messages over NAS signaling.

The MME node 206 may receive, via the RAN 202, the SMS over NAS request216 from the UE 200, and, at 218, the receipt of the SMS over NASrequest 216 from the UE 200 triggers the MME node 206 to register the UE200 with the CS network. In other words, by sending the SMS over NASrequest 216 to the MME node 206, the UE 200 is informing the MME node206 that the UE 200 wants to register with the CS network for acommunication session. Accordingly, in response to receiving the SMSover NAS request 216 from the UE 200, the MME node 206 may perform CSregistration 220 by registering the UE 200 with the CS network.

In some embodiments, one or more additional criteria are evaluatedbefore registering the UE 200 with the CS network. For example, acurrent utilization of the CS network may be evaluated to determine ifthere is capacity or bandwidth in the CS network to handle theto-be-registered UE 200. For example, in response to receiving the SMSover NAS request 216 from the UE 200, a determination may be made as toa number of UEs (and/or subscribers associated therewith) currentlyregistered with the CS network, and the CS registration 220 may beperformed for the UE 200 based at least in part on the number of UEscurrently registered with the CS network. For example, the number of UEscurrently registered with the CS network may be compared to a thresholdnumber, and if the number of presently-registered UEs satisfies (e.g.,meets, meets or exceeds) the threshold number, the UE 200 may not beregistered with the CS network due to limitations in bandwidth orcapacity of the CS network to handle additional UEs. If, however, thenumber of presently-registered UEs does not satisfy (e.g., does notmeet, meets but does not exceed) the threshold number, the UE 200 may beregistered with the CS network (i.e., CS registration 220 may beperformed).

In some embodiments, the CS registration 220 of the UE 200 (i.e.,registering the UE 200 with the CS network) may include sending, by theMME node 206, an ID associated with the UE 200 to the MSS 208. In someembodiments, the MME node 206 may send, to the UE 200, a message 226indicating that the SMS over NAS request 216 is accepted.

The UE 200 may conduct the communication session by transmitting andreceiving NAS messages via the RAT 204, the NAS messages carrying SMStext payloads (e.g., text, images, video clips, etc.). In particular,the UE 200 may send a SMS text message as a NAS request to the MME node206, the MME node 206 may forward the SMS text message to the MSS 208,and the MSS may forward the SMS text message to a Short Message ServiceCenter (SMSC) 222 so that the SMS text message is ultimately received bya terminating endpoint (e.g., a second UE of another user). In thereturn path, a SMS text message is sent by the SMSC 222 to the MSS 208,the MSS 208 may forward the SMS text message to the MME node 206, andthe MME node 206 may forward the SMS text message to the UE 200 as a NASresponse sent via the RAT 204. As shown in FIG. 2, this message routingpath may send SMS text messages over SGs interface. When thecommunication session is terminated, such as after a timeout periodexpires with no SMS text messages sent over NAS signaling, the UE 200may re-establish a connection for sending SMS text messages over IPsignaling of the PS network.

It can be appreciated that the techniques and systems described withreference to FIG. 2 allow for better management of the capacity of alegacy CS network, which may help while phasing out a CS network from acarrier's network infrastructure. For instance, the techniques andsystems of FIG. 2 may result in a number of subscribers registered witha CS network that is less than a number of subscribers registered with aPS network (e.g., a LTE network). In other words, utilization of the CSnetwork may be kept to a minimum by controlling CS registration 220per-device by using an “on-demand” CS registration technique where UEs200 are not registered with the CS network unless and until those UEs200 demand or request utilization of the CS network. The techniquesshown in FIG. 2 is useful for data-based communication sessions (or,non-voice-based communication session), such as SMS text messagingsessions, where the UE 200 is attempting to send SMS text messages overa preferred IP signaling layer of a PS network, and the UE 200 sends aSMS over NAS request 216 to request registration with the CS network toutilize NAS signaling for sending SMS text messages, thereby triggeringthe CS registration 220 at 218 and employing NAS messages for thetransport of SMS text payloads.

FIG. 3 is a diagram illustrating example signaling for implementingon-demand CS registration for a terminating UE 300 where the CSregistration is triggered by a notification of an incoming sessionrequest received from a Home Subscriber Server (HSS), the incomingsession request requesting establishment of a communication session overa CS network. It is to be appreciated that the UE 300 may be similar tothe UE 100 and/or the UE 200 described herein. Furthermore, the RANs 302may be similar to the RANs 102 and/or the RANs 202 described herein.Furthermore, the RATs 304 may be similar to the RATs 104 and/or the RATs204 described herein. Furthermore, the MME node 306 may be similar tothe MME node 106 and/or the MME node 206 described herein. Furthermore,the MSSs 308 may be similar to the MSS 108 and/or the MSS 208 describedherein.

In FIG. 3, at time=t₁, the UE 300 is shown as sending a combined attachrequest 310 to the MME node 306 of the telecommunications network. Forexample, a user of the UE 300 may power-on the UE 300, causing the UE300 to search for a preferred RAN 302(1) to which the UE 300 sends thecombined attach request 310. This combined attach request 310 may besimilar to the combined attach request 110 and/or the combined attachrequest 210 described herein.

The MME node 306 receives, via the first RAN 302(1), the combined attachrequest 310 from the UE 300, and responds by sending, to the UE 300, amessage 312 that acknowledges receipt of the request 310, and thatprovides an attach result (e.g., “attach accepted: combined”, “attachaccepted: EPS only”, or “attach rejected”). In the example of FIG. 3,like FIGS. 1 and 2, the message 312 indicates that the combined attachrequest 310 is accepted (e.g., attach accepted: combined). Of course,depending on the circumstances, the message 312 may include other attachresults, as described with reference to FIG. 1.

At 314 of FIG. 3, at time=t₁, when the UE 300 sends the combined attachrequest 310 to the MME node 306, the MME node 306 refrains fromregistering the UE 300 with the CS network, or, if the UE 300 happens tobe registered with the CS network when the combined attach request 310is received, the MME node 306 may de-register the UE 300 from the CSnetwork at 314. That is, the MME node 306 may determine whether the UE300 is, or is not, presently registered with the CS network at 314(e.g., by accessing a registry of UEs registered with the CS network),and, if registered, the MME node 306 may de-register the UE 300 from theCS network at 314. Regardless of whether the MME node 306 refrains fromregistering the UE 300 with the CS network or de-registers the UE 300from the CS network, the lack of CS registration of the UE 300 occursdespite the availability of a CS network (e.g., RAN 302(2) associatedwith RAT 304(2), such as a 2G/3G RAT) and despite the sending of themessage 312 indicating that the combined attach request 310 is accepted.In other words, the MME 306 is configured to “fake” the combined attachprocedure by indicating to the UE 300 that the UE 300 is registered witha CS network when, in fact, the UE 300 is not registered with a CSnetwork.

In FIG. 3, at time=t₁, and in response to receiving the combined attachrequest 310, the MME node 306 may send a message 316 to a homesubscriber server (HSS) 326 of the telecommunications network, themessage 316 including location information for updating a locationassociated with the UE 300. This location update message 316 may betransmitted to the HSS 326 using Diameter protocol over a Diameter (Cx)interface. The HSS 326 may be associated with a master database(sometimes referred to herein as an “HSS repository”) that maintainsdata pertaining to UEs, such as the UE 300, which have registered, orare in the process of registering, on the IMS network.

Similar to the description of FIG. 1, using the techniques and systemsof FIG. 3, the MME node 306 does not blindly register the UE 300 withthe CS network. Instead, the MME node 306 waits to register the UE 300with the CS network until a time at which it is demanded for the UE 300to utilize the CS network (e.g., to establish a communication session).FIG. 3 illustrates one example trigger event that may cause the UE 300to be registered with an available CS network in an on-demand fashionwhen the UE 300 is acting as a terminating UE (sometimes referred toherein as “MT UE”, “MT” meaning “mobile terminated” or “mobileterminating”).

In FIG. 3, at time=t₂, a first MSS 308(1) may receive an incomingsession request 332 (e.g., a voice call) originating from a second UE(not shown) to establish a communication session over a CS network withthe first UE 300. In this scenario, the second UE that originated thesession request 332 is the originating UE, and the first UE 300 shown inFIG. 3 is the terminating UE. The incoming session request 332 may bereceived by the first MSS 308(1) for various reasons, as describedherein. For example, the second UE may not have a VoIP capability or mayhave a VoIP capability disabled in user settings when a user of thesecond UE makes a call by dialing a phone number, causing the call to besetup over a CS network. As another example, the second UE may start atimer while setting up a VoIP call over a preferred RAT of a PS network,and if a timeout occurs before the second UE receives an expectednetwork response, the second UE may attempt to setup the call over theCS network. As yet another example, a network node may send a signal tothe second UE indicating that a VoIP call cannot be established.

In any case, in response to receiving the incoming session request 332,the first MSS 308(1) may send a request 334 to a Home Location Register(HLR) 336 of the telecommunications network, the request 334 requestingrouting information to route the incoming session request 332 to theappropriate network nodes that will ultimately allow for establishingthe communication session with the terminating UE 300. Instead ofrejecting this request 334 outright because the UE 300 is not presentlyregistered with the CS network, the HLR 336 may send the request 334 tothe HSS 326, or may otherwise notify the HSS 326 of the informationpertaining to the routing information request 334, and the HSS 326, withaccess to this information from the HLR 336, may send a notification 338to the MME node 306, the notification 338 indicating that there is anincoming session request 332 originating from a second UE to establish acommunication session over a CS network with the first UE 300. The HSS326 can identify the MME node 306 based at least in part on the locationupdate message 316 it previously received from the MME node 306 attime=t₁.

The MME node 306 may receive the notification 338 of the incomingsession request 332 from the HSS 326, and, at 318, the receipt of thenotification 338 of the incoming session request 332 from the HSS 326triggers the MME node 306 to register the UE 300 with the CS network. Inother words, by sending the notification 338 of the incoming sessionrequest 332 to the MIME node 306, the HSS 326 is informing the MME node306 that the first UE 300 will need to utilize the CS network for acommunication session with the second UE. Accordingly, in response toreceiving the notification 338 of the incoming session request 332 fromthe HSS 326, the MME node 306 may perform CS registration 320 byregistering the first UE 300 with the CS network. This CS registration320 may be similar to the CS registration 120 and/or the CS registration220 described herein.

In some embodiments, one or more additional criteria are evaluatedbefore registering the UE 300 with the CS network. For example, acurrent utilization of the CS network may be evaluated to determine ifthere is capacity or bandwidth in the CS network to handle theto-be-registered UE 300. For example, in response to receiving thenotification 338 of the incoming session request 332 from the HSS 326, adetermination may be made as to a number of UEs (and/or subscribersassociated therewith) currently registered with the CS network, and theCS registration 320 may be performed for the UE 300 based at least inpart on the number of UEs currently registered with the CS network. Forexample, the number of UEs currently registered with the CS network maybe compared to a threshold number, and if the number ofpresently-registered UEs satisfies (e.g., meets, meets or exceeds) thethreshold number, the UE 300 may not be registered with the CS networkdue to limitations in bandwidth or capacity of the CS network to handleadditional UEs. If, however, the number of presently-registered UEs doesnot satisfy (e.g., does not meet, meets but does not exceed) thethreshold number, the UE 300 may be registered with the CS network(i.e., CS registration 320 may be performed). In some embodiments, theCS registration 320 of the UE 300 (i.e., registering the UE 300 with theCS network) may include sending, by the MME node 306, an ID 322associated with the UE 300 to a second MSS 308(2).

In response to the CS registration 320, the second MSS 308(2) mayperform an operation(s) that allows the second MSS 308(2) to receive therelevant information about the incoming session request 332 from thefirst MSS 308(1) that received the incoming session request 332. Forexample, the second MSS 308(2) may send a message 340 to the HLR 336,the message 340 including location information for updating a locationassociated with the UE 300 within the HLR 336.

The HLR 336 may receive the location update message 340 from the secondMSS 308(2) and may respond by sending a routing information response 342to the first MSS 308(1), which had previously requested routinginformation from the HLR 336 via the request 334. This routinginformation provided in the response 342 may include information thatallows the first MSS 308(1) to identify the appropriate network node(namely, the second MSS 308(2)) for establishing the communicationsession with the UE 300. Accordingly, the first MSS 308(1) may provideinformation to the second MSS 308(2) based on the routing information itreceived in the response 342 from the HLR 336, and the MME node 306 mayreceive, from the second MSS 308(2), information 324 that is usable toestablish the communication session over the CS network for the first UE300.

Using the information 324 received from the second MSS 308(2), the MMEnode 306 may send a page request 344 to the first UE 300 to establishthe communication session over the CS network. This page request 344 maybe sent to the UE 300 via the preferred RAN 302(1) associated with thepreferred RAT 304(1) (e.g., a 5G RAT, a 4G LTE RAT, etc.). The pagerequest 344 may include the information 324 the MME node 306 receivedfrom the second MIMS 308(2), which is usable by the UE 300 to establishthe communication session over the CS network. For example, theinformation 324—received from the second MSS 308(2) and forwarded by theMME node 306 to the UE 300—may include an identifier and/or an addressof the RAN 302(2) associated with a legacy RAT 304(2) of the CS network,which allows the UE 300 to redirect 328 from the preferred RAN 302(1) tothe RAN 302(2) associated with a legacy RAT 304(2) (e.g., 2G/3G RAT) ofthe CS network. This may cause the UE 300 to switch from a VoIP call toa CS call, for example. The RAN 302(1) may redirect 328 the UE 300 tothe RAN 302(2), such as by sending an IRAT handover command to the UE300, by cell reselection, or any other suitable redirection 328technique.

The UE 300 may conduct the communication session over the CS networkusing the legacy RAT 304(2), and when the communication session isterminated, such as when a user hangs up a call, a network node (e.g.,the first MSS 308(1), the RAN 302(2), etc.) and/or logic of the UE 300may cause the UE 300 to return 330 to the preferred RAN 302(1)associated with the preferred RAT 304(1) of the PS network. Thisso-called “fast return” 330 logic redirects the UE 300 to the PS networkand prevents the UE 300 from staying camped on the legacy RAT 304(2) forlonger than it needs to be there. That is, once the UE 300 is finishedusing the legacy RAT 304(2) of the CS network for the communicationsession, the UE 300 is redirected back (e.g., via return 330) to thepreferred RAT 304(1) of the PS network.

It can be appreciated that the techniques and systems described withreference to FIG. 3 allow for better management of the capacity of alegacy CS network, which may help while phasing out a CS network from acarrier's network infrastructure. For instance, the techniques andsystems of FIG. 3 may result in a number of subscribers registered witha CS network that is less than a number of subscribers registered with aPS network (e.g., a 5G network, a 4G LTE network, etc.). In other words,utilization of the CS network may be kept to a minimum by controlling CSregistration 320 per-device by using an “on-demand” CS registrationtechnique where UEs 300 are not registered with the CS network unlessand until it is demanded or requested that those UEs 300 utilize the CSnetwork. The techniques shown in FIG. 3 is useful for voice-basedcommunication sessions, such as phone calls, where the UE 300 is aterminating UE 300 of session that is being established over the CSnetwork. It is also to be appreciated, however, that techniques similarto those shown in FIG. 3 may be used for data-based communicationsessions (or non-voice-based communication sessions), such as SMS textmessaging sessions, where the UE 300 may be receiving a SMS text messageover NAS signaling, similar to the scenario of FIG. 2, but with the UE300 as a terminating UE. In this case, the incoming session request 332may represent a request to establish a SMS text messaging session withthe UE 300, and the page request 344 may be a SMS over NAS response(e.g., a Downlink NAS Transport message) sent by the MME node 306 to theUE 300 in order to transport SMS text message payloads with NASmessages, instead of using an IP-based message for transport of SMS textmessage payloads.

It is also to be appreciated that, instead of a “network-controlled”approach to on-demand CS registration, as described herein, a UE-centricapproach may be taken to modify logic of the UE itself to control CSregistration of UEs in an on-demand fashion. Such an approach mayinvolve changing the way that attach requests are sent to the MME 306(e.g., a new form of attach request that prevents the UE from beingblindly registered with a CS network that is available to the UE).

The processes described in this disclosure may be implemented by thearchitectures described herein, or by other architectures. Theseprocesses are illustrated as a collection of blocks in a logical flowgraph. Some of the blocks represent operations that can be implementedin hardware, software, or a combination thereof. In the context ofsoftware, the blocks represent computer-executable instructions storedon one or more computer-readable storage media that, when executed byone or more processors, perform the recited operations. Generally,computer-executable instructions include routines, programs, objects,components, data structures, and the like that perform particularfunctions or implement particular abstract data types. The order inwhich the operations are described is not intended to be construed as alimitation, and any number of the described blocks can be combined inany order or in parallel to implement the processes. It is understoodthat the following processes may be implemented on other architecturesas well.

FIG. 4 illustrates a flowchart of an example process 400 for performingCS registration for a UE, on-demand. The process 400 is described, byway of example, with reference to the previous figures. The process 400may be implemented by a system (e.g., the system 800 of FIG. 8) thatincludes a MME node 106/206/306, as described herein. Accordingly,reference is made to a MME node 106/206/306 in describing the process400, as the MME node 106/206/306 may perform at least some of theoperations of the process 400.

At 402, a MME node 106/206/306 of a telecommunications network mayreceive a combined attach request 110/210/310 from a UE 100/200/300. Forexample, a user of the UE 100/200/300 may power-on the UE 100/200/300,causing the UE 100/200/300 to search for a preferred RAN 102/202/302 towhich the UE 100/200/300 sends the combined attach request 110/210/310.This combined attach request 110/210/310 may be sent by the UE 100 aspart of a combined attach procedure (e.g., as defined in 3GPP TS 24.301)to register the UE 110/210/310 with both a CS network and a PS network,as described herein. The combined attach request 110/210/310 may betransmitted using NAS protocol.

At 404, the MME node 106/206/306 may send, to the UE 100/200/300, amessage 112/212/312 indicating that the combined attach request110/210/310 is accepted. For example, the message 112/212/312 mayinclude an attach result (e.g., “attach accepted: combined”), indicatingthat the combined attach request 110/210/310 is accepted.

At 406, the MME node 106/206/306 may determine whether the UE100/200/300 is presently registered with a CS network. For example, theMME node 106/206/306 may access a registry of UEs registered with the CSnetwork to make this determination at block 406. If the UE 100/200/300is presently registered with a CS network (e.g., if the MME node106/206/306 identifies an identifier in the registry that matches anidentifier received from the UE 100/200/300), the process 400 may followthe “YES” route from block 406 to block 408.

At 408, the MME node 106/206/306 may de-register the UE 100/200/300 fromthe CS network, based on the UE 100/200/300 being presently registeredwith the CS network. For example, the MME node 106/206/306 may remove ordelete (or cause to be removed or deleted) an identifier of the UE fromthe registry accessed by the MME node 106/206/306.

At 410, after de-registering the UE 100/200/300 from the CS network, or,if the MME node 106/206/306 determines, at block 406, that the UE100/200/300 is not presently registered with a CS network, causing theprocess 400 to follow the “NO” route from block 406 to block 410, theMME node 106/206/306 may determine whether CS registration 120/220/320is triggered. As shown by block 412, CS registration 120/220/320 can betriggered in several ways, depending on the operating mode of the UE100/200/300 (e.g., whether the UE 100/200/300 is operating as a MO UE ora MT UE) and/or the type of communication session (e.g., a voice-basedcommunication session or a data-based communication session, such as SMStext messaging session).

For example, the determination at block 410 as to whether CSregistration 120/220/320 is triggered may include the MME node106/206/306 receiving a service request from the UE 100/200/300, theservice request having been sent using NAS protocol. Receiving a servicerequest from the UE 100/200/300 may include receiving, by the MME node106/206/306, an ESR 116 from the UE 100/200/300. An ESR 116 may indicatethat the UE 100/200/300 is requesting to fall back to a CS network for avoice-based communication session. Receiving a service request from theUE 100/200/300 may include receiving, by the MME node 106/206/306, a SMSover NAS request 216 from the UE 100/200/300, such as an Uplink NASTransport message. These examples pertain to a UE 100/200/300 operatingas an originating UE (or, MO UE). If the UE 100/200/300 is operating asa terminating UE (or, MT UE), the determination at block 410 as towhether CS registration 120/220/320 is triggered may include the MMEnode 106/206/306 receiving, from a HSS 326, a notification 338 of anincoming session request 332 originating from a second UE to establish acommunication session over a CS network with the UE 100/200/300.

If CS registration 120/220/320 is not triggered at block 410, theprocess 400 may follow the “NO” route from block 410, causing theprocess 400 to iterate the determination at block 410. If CSregistration 120/220/320 is triggered at block 410, the process 400 mayfollow the “YES” route from block 410 to block 414.

At 414, in response to the CS registration 120/220/320 being triggered(e.g., receiving of a NAS-based service request, such as an ESR 116 or aSMS over NAS request 216, from the UE 100/200/300, receiving anotification 338 of an incoming session request from the HSS 326, etc.),the MME node 106/206/306 may register the UE 100/200/300 with the CSnetwork. As shown by sub-block 416, this registration step may includethe MME node 106/206/306 sending an ID associated with the UE100/200/300 to a MSS 108/208/308. Accordingly, the UE 100/200/300 isregistered with the CS network on-demand in response to a trigger event,rather than the UE 100/200/300 being blindly registered at the time ofreceiving the combined attach request at block 402.

FIG. 5 illustrates a flowchart of an example process 500 for returning aUE back to a PS network after a communication session over a CS networkhas terminated. The process 500 is described, by way of example, withreference to the previous figures. Furthermore, as shown by off-pagereference “A” in FIGS. 4 and 5, the process 500 may continue from block414 of FIG. 4, after the MME node 106/206/306 registers the UE100/200/300 with the CS network.

At 502, a communication session may be established for the UE100/200/300. As described herein, for a voice-based communicationsession, the communication session may be established over the CSnetwork with which the UE 100/200/300 was previously registered. Forexample, as shown by sub-block 504, the MME node 106/206/306 (or adifferent network node, such as a RAN 102/202/302) may redirect UE froma PS network to the CS network. In the terminating UE (MT UE) scenario,this may include the MME node 106/206/306 sending a page request 344 tothe UE 100/200/300, as shown by sub-block 506, the page request 344 forestablishing the voice-based communication session over the CS network.For a data-based communication session (e.g., a SMS text messagingsession), the establishment of the communication session for the UE100/200/300 at block 502 may include establishing a connection over aNAS signaling layer to allow the UE 100/200/300 to send SMS textmessages using NAS protocol.

At 508, the communication session may be terminated. For example, avoice-based communication session (e.g., a call) established over the CSnetwork may be terminated. Terminating the communication session mayoccur at block 508 in response to a party of the communication sessionproviding user input to his/her UE, for example by hanging up a call.

At 510, the UE 100/200/300 may be redirected from the CS network back tothe PS network based at least in part on terminating the communicationsession at block 508. This so-called “fast return” logic redirects theUE 100/200/300 to the PS network and prevents the UE 100/200/300 fromstaying camped on the legacy RAT 104(2)/304(2) for longer than it needsto be there. That is, once the UE 100/200/300 is finished using thelegacy RAT 104(2)/304(2) of the CS network for the communicationsession, the UE 100/200/300 is redirected back to a preferred RAT104(1)/304 of the PS network

It is to be appreciated that, if the UE 100/200/300 sends a second,subsequent combined attach request 110/210/310 to the MME 106/206/306 atany point, such as after the UE 100/200/300 is moved to anothergeographic location, after power cycling the UE 100/200/300, etc., theprocess 400 may iterate, whereby the UE 100/200/300, if still registeredwith the CS network, will be de-registered at block 408 of the process400. For example, following block 510, the MME node 106/206/306 mayreceive, at block 402, a second combined attach request 110/210/310 fromthe UE 100/200/300, send, at block 404, a second message 112/212/312 tothe UE 100/200/300 indicating that the second combined attach request110/210/310 is accepted, determine, at block 406, that the UE100/200/300 is presently registered with the CS network, and de-registerthe UE 100/200/300 from the CS network at block 408.

FIG. 6 illustrates a flowchart of an example process 600 for registeringa UE with a CS network based on a capacity metric of the CS network. Theprocess 600 is described, by way of example, with reference to theprevious figures.

At 602, a determination is made as to whether CS registration120/220/320 is triggered for a UE 100/200/300. For example, CSregistration 120/220/320 may be triggered if the MME node 106/206/306receives a service request from the UE 100/200/300 that was sent usingNAS protocol (e.g., a ESR 116 or a SMS over NAS request 216), or if theMME node 106/206/306 receives, from the HSS 326, a notification 338 ofan incoming session request 332 (e.g., an incoming call over CS).

At 604, a number of UEs currently registered with the CS network may bedetermined by the MME node 106/206/306. For example, the MME node106/206/306 may access a registry of UEs to determine a number of UEscurrently/presently registered with the CS network.

At 606, the number of UEs currently registered with the CS network maybe compared to a threshold number to determine whether the threshold issatisfied. The threshold may be satisfied if the number of registeredUEs meets or exceeds the threshold number, or if the number ofregistered UEs strictly exceeds the threshold number. For instance,there may be a limit to the number of UEs that the CS network can handleat any given time. Hence, the number of UEs currently registered withthe CS network can be thought of as a capacity metric, and a carrier whoowns and/or operates the CS network may set an appropriate thresholdnumber of UEs that it wants to allow to be registered with the CSnetwork at any given moment, which helps to manage the utilization andcapacity of the CS network. If the threshold number is not satisfied atblock 606 (e.g., if the number of registered UEs is below the thresholdnumber, or at or below the threshold number), the process 600 may followthe “NO” route from block 606 to block 608.

At 608, based at least in part on the number of UEs currently registeredwith the CS network, the MME node 106/206/306 may register the UE100/200/300 with the CS network. If the threshold number is satisfied atblock 606 (e.g., if the number of registered UEs exceeds the thresholdnumber, or meets or exceeds the threshold number), the process 600 mayfollow the “YES” route from block 606 to block 610.

At 610, the MME node 106/206/306 may refrain from registering the UE100/200/300 with the CS network. This may help manage the capacity ofthe CS network by limiting the number of UEs that are registered withthe CS network at any given moment, which may be useful when phasing outa CS network.

FIG. 7 illustrates a flowchart of an example process 700 forestablishing a communication session for a terminating UE that has beenregistered with a CS network, on-demand. The process 700 is described,by way of example, with reference to the previous figures. Furthermore,as shown by off-page reference “A” in FIGS. 4 and 7, the process 700 maycontinue from block 414 of FIG. 4, after the MME node 106/206/306registers the UE 100/200/300 with the CS network.

At 702, after the MME 306 registers the UE 300 with the CS network bysending an ID of the UE 300 to a (first) MSS 308(2), the (first) MSS308(2) may send a location update 340 to a HLR 336. This may provideupdated location information for the UE 300 that was registered with theCS network. The HLR 336 may send routing information 342 to a second MSS308(1) that received the incoming session request 332 originated by asecond UE (MO UE), and the second MSS 308(1) may send information to the(first) MSS 308(2).

Accordingly, at 704, the (first) MSS 308(2) may receive, from the secondMSS 308(1), information associated with the incoming session request332. This is based on the second MSS 308(1) having received the routinginformation 342 from the HLR 336.

At 706, the (first) MSS 308(2) may send, to the MME node 306, theinformation, or different information 324 that is based on theinformation, to include in a page request 344 to the UE 300 forestablishing the communication session over the CS network. As shown bythe off-page reference “B” in FIGS. 5 and 7, the process 500 maycontinue from block 706 of the process 700, such as by establishing acommunication session for the UE 300 at block 502.

FIG. 8 is a block diagram of an example system 800 configured toimplement on-demand CS registration for a UE. The system 800 may includeone or more network nodes of a telecommunications network. For example,the system 800 may represent a MME node(s) 106/206/306. In someembodiments, the system 800 may represent multiple different nodesincluding the MME node(s) 106/206/306 and one or more additional networknodes including, without limitation, a RAN(s) 104/204/304, a MSS(s)108/208/308, a HSS(s) 326, a HLR(s) 336, and/or a SMSC(s) 222.

As shown, the system 800 may include one or more processors 802 and oneor more forms of computer-readable memory 804. The system 800 may alsoinclude additional storage devices. Such additional storage may includeremovable storage 806 and/or non-removable storage 808.

The system 800 may further include input devices 810 and output devices812 communicatively coupled to the processor(s) 800 and thecomputer-readable memory 804. The system 800 may further includecommunications interface(s) 816 that allow the system 800 to communicatewith other computing devices 818 (e.g., UEs, other network nodes, etc.)such as via a network. The communications interface(s) 818 mayfacilitate transmitting and receiving wired and/or wireless signals overany suitable communications/data technology, standard, or protocol, asdescribed herein.

In various embodiments, the computer-readable memory 804 comprisesnon-transitory computer-readable memory 804 that generally includes bothvolatile memory and non-volatile memory (e.g., random access memory(RAM), read-only memory (ROM), erasable programmable read-only memory(EEPROM), Flash Memory, miniature hard drive, memory card, opticalstorage, magnetic cassettes, magnetic tape, magnetic disk storage orother magnetic storage devices, or any other medium). Thecomputer-readable memory 804 may also be described as computer storagemedia and may include volatile and nonvolatile, removable andnon-removable media implemented in any method or technology for storageof information, such as computer readable instructions, data structures,program modules, or other data. Computer-readable memory 804, removablestorage 806 and non-removable storage 808 are all examples ofnon-transitory computer-readable storage media. Computer-readablestorage media include, but are not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, compact disc read-only memory(CD-ROM), digital versatile disks (DVD) or other optical storage,magnetic cassettes, magnetic tape, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to storethe desired information and which can be accessed by the system 800. Anysuch computer-readable storage media may be part of the system 800.

The memory 804 can include an on-demand CS registration component(s)820, which may represent computer-executable instructions (or logic)that, when executed, by the processor(s) 802, perform the various actsand/or processes disclosed herein.

The environment and individual elements described herein may of courseinclude many other logical, programmatic, and physical components, ofwhich those shown in the accompanying figures are merely examples thatare related to the discussion herein.

The various techniques described herein are assumed in the givenexamples to be implemented in the general context of computer-executableinstructions or software, such as program modules, that are stored incomputer-readable storage and executed by the processor(s) of one ormore computers or other devices such as those illustrated in thefigures. Generally, program modules include routines, programs, objects,components, data structures, etc., and define operating logic forperforming particular tasks or implement particular abstract data types.

Other architectures may be used to implement the describedfunctionality, and are intended to be within the scope of thisdisclosure. Furthermore, although specific distributions ofresponsibilities are defined above for purposes of discussion, thevarious functions and responsibilities might be distributed and dividedin different ways, depending on circumstances.

Similarly, software may be stored and distributed in various ways andusing different means, and the particular software storage and executionconfigurations described above may be varied in many different ways.Thus, software implementing the techniques described above may bedistributed on various types of computer-readable media, not limited tothe forms of memory that are specifically described.

We claim:
 1. A method comprising: receiving, by a mobility managemententity (MME) node of a telecommunications network, a combined attachrequest from a user equipment (UE); sending, by the MME node, to the UE,a message indicating that the combined attach request is accepted;determining, by the MME, that the UE is presently registered with afirst circuit-switched (CS) network; de-registering, by the MME and atleast in part in response to receiving the combined attach request, theUE from the first CS network; receiving, by the MME node, an extendedservice request (ESR) from the UE indicating that the UE is requestingto fall back to a second CS network; and in response to receiving thecombined attach request and the ESR from the UE: registering the UE withthe second CS network; and establishing the voice-based communicationsession over the second CS network.
 2. The method of claim 1, furthercomprising: terminating the voice-based communication session over theCS network; and redirecting the UE from the second CS network to apacket-switched (PS) network based at least in part on terminating thevoice-based compunction session.
 3. The method of claim 1, wherein:receiving, by the MME node, a second combined attach request from theUE; sending, by the MME node, to the UE, a second message indicatingthat the second combined attach request is accepted; determining thatthe UE is presently registered with the second CS network; andde-registering, by the MME node, the UE from the second CS network basedon the UE being presently registered with the second CS network.
 4. Themethod of claim 1, further comprising: in response to the receiving ofthe ESR from the UE, determining a number of UEs currently registeredwith the second CS network, wherein the registering the UE with thesecond CS network is based at least in part on the number of UEscurrently registered with the second CS network.
 5. The method of claim1, wherein the ESR received from the UE was sent using Non-AccessStratum (NAS) protocol.
 6. A system comprising: one or more processors;and memory storing computer-executable instructions that, when executedby the one or more processors, cause the system to: receive a combinedattach request from a user equipment (UE); determine that the UE ispresently registered with a first circuit-switched (CS) network;de-register, at least in part in response to receiving the combinedattach request, the UE from the first CS network; send, to the UE, amessage indicating that the combined attach request is accepted; receivea service request from the UE, the service request having been sentusing Non-Access Stratum (NAS) protocol; and in response to receivingthe combined attach request and the service request from the UE,register the UE with a second circuit-switched (CS) network.
 7. Thesystem of claim 6, wherein the one or more processors and the memorystoring the computer-executable instructions are implemented on amobility management entity (MME) node of a telecommunications network.8. The system of claim 7, wherein registering the UE with the CS networkcomprises sending, by the MME node, an identifier (ID) associated withthe UE to a mobile switching station (MSS) of the second CS network. 9.The system of claim 6, wherein the service request received from the UEcomprises an extended service request (ESR), and wherein thecomputer-executable instructions, when executed by the one or moreprocessors, further cause the system to establish a voice-basedcommunication session over the second CS network in response toregistering the UE with the second CS network.
 10. The system of claim9, wherein the computer-executable instructions, when executed by theone or more processors, further cause the system to: terminate thevoice-based communication session over the second CS network; andredirect the UE to a packet-switched (PS) network based at least in parton terminating the voice-based communication session.
 11. The system ofclaim 6, wherein the service request received from the UE comprises aShort Message Service (SMS) over NAS request.
 12. The system of claim 6,wherein the computer-executable instructions, when executed by the oneor more processors, further cause the system to: receive a secondcombined attach request from the UE; send, to the UE, a second messageindicating that the second combined attach request is accepted; andde-register the UE from the second CS network.
 13. The system of claim6, wherein the computer-executable instructions, when executed by theone or more processors, further cause the system to: in response toreceiving the service request from the UE, determine a number of UEscurrently registered with the second CS network, wherein registering theUE with the second CS network is based at least in part on the number ofUEs currently registered with the second CS network.
 14. A methodcomprising: receiving, by a mobility management entity (MME) node of atelecommunications network, a combined attach request from a first userequipment (UE); sending, by the MME node, to the first UE, a messageindicating that the combined attach request is accepted; refraining, atleast in part in response to receiving the combined attach request, fromregistering the UE with a circuit-switched (CS) network; receiving, bythe MME node, from a Home Subscriber Server (HSS), a notification of anincoming session request originating from a second UE to establish acommunication session over the CS network with the first UE; and inresponse to receiving the attach request and the notification from theHSS, registering, by the MME node, the first UE with the CS network. 15.The method of claim 14, wherein the communication session is avoice-based communication session, the method further comprisingsending, by the MME node, a page request to the first UE forestablishing the voice-based communication session over the CS network.16. The method of claim 15, further comprising: terminating thevoice-based communication session over the CS network; and redirectingthe first UE to a packet-switched (PS) network based at least in part onterminating the voice-based communication session.
 17. The method ofclaim 14, further comprising: receiving, by the MME node, a secondcombined attach request from the first UE; sending, by the MME node, tothe first UE, a second message indicating that the second combinedattach request is accepted; and de-registering, by the MME node, the UEfrom the CS network.
 18. The method of claim 14, further comprising: inresponse to the receiving of the notification from the HSS, determininga number of UEs currently registered with the CS network, wherein theregistering the first UE with the CS network is based at least in parton the number of UEs currently registered with the CS network.
 19. Themethod of claim 14, wherein the registering the first UE with the CSnetwork comprises sending, by the MME node, an identifier (ID)associated with the first UE to a mobile switching station (MSS). 20.The method of claim 19, further comprising, after the sending the IDassociated with the first UE to the MSS: sending, by the MSS, a locationupdate to a Home Location Register (HLR); receiving, by the MSS, from asecond MSS, information associated with the incoming session request;and sending, by the MSS, to the MME node, the information, or differentinformation based on the information, to include in a page request tothe first UE for establishing the communication session over the CSnetwork.